Manage your subscription

Gigantic solar storms slash ozone levels

The gigantic solar storms of November 2003 severely depleted the ozone layer above the Arctic for as long as eight months, suggest newly released satellite observations. Ozone levels had reduced to just 40% of normal spring levels in 2004.

“We have never seen ozone close to this level in the northern hemisphere,” says Cora Randall, a researcher with the Laboratory for Atmospheric and Space Physics at the University of Colorado at Boulder, US, and one of the study team.

Ozone in Earth’s stratosphere protects the planet against harmful ultraviolet radiation. Most of the gas lies in the lower- and mid-stratosphere, where observations have shown a thinning above the poles caused mainly by man-made chemicals, such as chlorofluorocarbons (CFCs).

Now, Randall and her team have used seven satellites to study ozone in the upper region of the stratosphere, which contains about one-fifth of the stratosphere’s supply and lies at an altitude of about 40 kilometres. Their observations show that nature can mimic manmade damage by increasing levels of nitrogen oxides in the atmosphere, which lead to the breakdown of ozone.

Advertisement

Electron funnel

The domino-like effect began in October and November 2003, when the Sun unleashed a record barrage of radiation and charged particles toward Earth.

The planet’s magnetic field funnelled some of the storm’s electrons into the upper atmosphere above the poles. The electrons hit nitrogen molecules there, breaking some of them into nitrogen ions. Those reactive atoms then combined with nearby oxygen molecules to form molecules of nitrogen oxide – levels of which rose in November and December 2003, according to the satellite data.

Finally, downward-blowing winds in a polar vortex above the Arctic pushed these molecules into the stratosphere. There, each nitrogen oxide molecule could rip apart hundreds of ozone molecules, just as CFCs do. The effect remained even into July 2004, according to Randall’s observations.

Sunlight saving

But ozone was not affected in the upper stratosphere over the Antarctic because of a seasonal effect, Randall notes. Summer sunlight shining over the South Pole during the solar storm broke apart nitrogen oxide molecules there, preventing them from going on to destroy ozone.

Randall hopes the findings will help scientists better understand the recovery of the ozone layer. Charles Jackman, an atmospheric scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, US, agrees. “In order to understand man-made changes to ozone, you really have to understand the natural changes,” he told New Scientist.

Jackman says he has also detected ozone depletion by protons in the 2003 solar storm. Protons, which are much heavier than electrons, can fall to the stratosphere with no help from air currents. He will publish his results in a future study.